1. Field of the Invention
The present invention relates generally to dynamic multicast service in a wavelength division multiplexed passive optical network (WDM-PON) and, more particularly, to a method of dynamically managing multicast groups and allocating multicast service wavelengths for maximal channel efficiency by ascertaining the channel share index of multicast groups that occupy a limited broadcasting wavelength when the multicast groups are changed in a hybrid type WDM-PON.
2. Description of the Prior Art
Communication having a point-to-point information exchange function has limited and personal effects because information flow occurs bi-directionally and in connection with specific individuals. In contrast, broadcasting having a point-to-multipoint information distribution function is characterized in that information flow occurs uni-directionally and information is shared by a plurality of subscribers.
Technology fields for providing broadcasting service and communication service at the same time through a communication network so as to accommodate the broadcasting service on behalf of existing communication carriers includes a Photonic Local Access Network (PLANET), which is a project to evolve a subscriber line to a broadband network in the Advanced Communications Technologies and Services (ACTS) project that is now being promoted in Europe, and Internet broadcasting, into which media, communication and broadcasting are converging.
In the ACTS-PLANET, SuperPON capable of reducing investment cost has been developed. SuperPON has a downstream transfer rate of 2.5 Gbps and an upstream transfer rate of 311 Mbps. Such SuperPON aims to provide subscribers with High Definition Television (HDTV) class services, such as Video on Demand (VoD), that have a very high downstream transfer rate. The signals of SuperPON are separated by a WDM filter. It should be noted that a PLANET amplified splitter includes an optical amplifier and an optical splitter, similar to those of a conventional Asynchronous Transfer Mode Passive Optical Network (ATM-PON). SuperPON has developed toward the improvement of a split ratio and a transfer capacity in an existing ATM-PON or Ethernet-PON.
As the transfer rate of the Internet gradually increases with the development and introduction of subscriber network technology, Internet broadcasting has changed to the form of using a streaming technology that plays an audio file or a video file while directly receiving the video or audio file. Currently, Internet broadcasting is in the process of changing from Asymmetric Digital Subscriber Line (ADSL) to Fiber-to-the-Home (FTTH) to expand the bandwidth of the access line. Korean communication carriers have made a variety of efforts to create new business opportunities via the Internet broadcasting service. It is expected that regular Internet broadcasting service will be launched soon.
In recent years, Internet traffic has exhibited an exponential increase in capacity due to the advent and popularization of a broadband application that provides high-quality audio and image data to service subscribers in real time. More particularly, with the advent of integrated network service that is intended to provide a communication-broadcasting convergence service through a single data transmission network, it is expected that the trend toward increased traffic will continue. Such a broadband service can be accommodated without significant burden in a backbone network or a metropolitan area network in which an increase in available capacity has been continuously achieved. However, a current subscriber network structure has many problems providing such real-time broadband service due to a narrow bandwidth per subscriber and the coexistence of various protocols.
The FTTH-based optical subscriber network project that is now being promoted aims to provide an optical technology-based broadband transmission bandwidth by deploying optical fiber between individual service subscribers and a central office. For this purpose, related technologies, such as an optical line installation technology, a Wavelength Division Multiplexing (WDM) technology, an optical element technology and an optical line distribution technology, for constructing an efficient and economical optical subscriber network based on optical technologies that have been used in an existing backbone have been rapidly developed. Research into ATM and Ethernet-based PON on a single star type subscriber network has been actively conducted, and is reaching a commercialization stage now. However, it is expected that the PON employing Time Division Multiplexing (TDM) will be developed toward a WDM-PON that allocates an independent wavelength to each subscriber while satisfying a desired bandwidth, due to the limitation in transmission capacity. Research into the WDM-PON is being actively conducted in U.S.A., Japan, Europe and elsewhere.
The WDM-PON is an optical distribution structure that can provide gigabit-class large-capacity data service without burden because an individual wavelength is allocated to each subscriber. More particularly, a hybrid type WDM-PON in which all the Optical Network Terminals (ONTs) of the network share a broadcasting channel, in addition to an individual data channel, is highly advantageous to the future accommodation of a broadcasting type multicast service because all the data are physically distributed to all the ONTs in an optical layer.
The FTTH WDM-PON aims to allocate sufficient bandwidth for the provision of a variety of services by providing an optical link to an ONT that is a termination device in a subscriber home. In this case, the ONT becomes an independent individual service termination point where the traffic and concentration of other subscribers are not achieved, unlike the Optical Network Unit (ONU) of a Fiber To The Curb (FTTC) network. Accordingly, the pattern of actual service traffic between an Optical Line Terminal (OLT) and the ONT exhibits very dynamic variation in bandwidth, not long-term consistent duration of bandwidth, based on the pattern of the Internet use of a user. This trend is more distinct in data services, such as common file transfer, image communication and high-quality VoD, than in broadcasting services in which a request for unidirectional bandwidth from a multicast server to an ONT is continuous. Therefore, the OLT within the hybrid type WDM-PON separates a consistent broadcasting service and a typical data service from each other and transmits them using different wavelengths, thus preventing the quality of the broadcasting service from being degraded due to the data service. Further, the OLT within the hybrid type WDM-PON manages multicasting and groups per port so that a broadcasting channel can be maximally shared within a limited bandwidth. Basically, the OLT monitors the addition and removal of multicast groups between the multicast router and the ONT using Internet Group Management Protocol (IGMP) snooping. When a new broadcasting service channel is established between them, its transmission is achieved using a shared optical broadcasting wavelength. Since such broadcasting data frames are distributed to all ONTs by a downstream optical splitter in a physical layer, an ONT that belongs to a corresponding group can receive the frame simply through filtering. It is thus possible to increase the share index of resources within the network.
In the case in which the OLT allocates the broadcasting channel in this First Come First Service (FCFS) mode, however, if all of the broadcasting wavelength is occupied by existing multicast groups, there occurs a problem in that a service request by a new multicasting group cannot be made using the broadcasting wavelength at a specific time point due to the bandwidth of a limited broadcasting wavelength. In this case, the OLT carries out multicasting using an independent data wavelength of each ONT. This is the same as the point-to-point multicasting mode within a conventional switch. If the number of service ONTs of the multicast service provided using the broadcasting type optical wavelength is smaller than the number of ONTs within the multicast group that employs the data optical wavelength, this results in the waste of a shared channel. As a result, the advantages of the hybrid structure are not properly made use of.
As described above, an efficient management scheme for accommodating a large number of broadcasting type multicast services and data services within the bandwidth of a limited broadcasting wavelength has not yet been proposed. Particularly, a scheme for efficiently accommodating multicast services within limited resources has not yet been proposed.
Meanwhile, U.S. Pat. Appl. Publication No. 2004/0184806 (entitled “Wavelength Division Multiplexing-Passive Optical Network capable of Integrating Broadcast and Communication Services”) discloses a PON that transmits a converged digital broadcasting and communication service using WDM. Further, U.S. Pat. Appl. Publication No. 2003/0123453 (entitled “Method and Apparatus of Directing Multicast Traffic in an Ethernet MAN”) discloses a method of managing a two-layer multicast group and a virtual LAN through an IGMP packet in an Ethernet switch so that even hosts that do not support Generic Attribute Registration (GARP) Multicast Registration Protocol (GMRP) and GARP Virtual Local Area Network (VLAN) Registration Protocol (GVRP) can participate in a desired two-layer multicast group and a virtual LAN of the Ethernet using the IGMP packet of the IP layer. Moreover, International Publication Number WO 98/048343 (entitled “System, Device, and Method for Managing Multicast Group Memberships in a Multicast Network”) discloses a system, device, and method for offloading the multicast routing protocols from local routers in a multicast network.
The preceding patents, however, do not disclose technology in which channel efficiency for an individual multicast group that employs the broadcasting wavelength within the bandwidth of a limited broadcasting wavelength in a WDM-PON is maximized. In particular, they do not present a method for multicast group management and wavelength allocation on a service basis for maximizing the service efficiency of multicast groups.